feat(oauth): add OAuth session caching to prevent multiple authentication attempts

readme.md

@@ -449,6 +449,35 @@ const accounts = await bunq.getAccounts();
 
 // According to bunq documentation: 
 // "Just use the OAuth Token (access_token) as a normal bunq API key"
+
+// OAuth Session Caching (v3.0.9+)
+// The library automatically caches OAuth sessions to prevent multiple authentication attempts
+
+// Multiple instances with the same OAuth token will reuse the cached session
+const bunq1 = new BunqAccount({
+  apiKey: 'your-oauth-access-token',
+  deviceName: 'OAuth App Instance 1',
+  environment: 'PRODUCTION',
+  isOAuthToken: true
+});
+
+const bunq2 = new BunqAccount({
+  apiKey: 'your-oauth-access-token',  // Same token
+  deviceName: 'OAuth App Instance 2',
+  environment: 'PRODUCTION',
+  isOAuthToken: true
+});
+
+await bunq1.init();  // Creates new session
+await bunq2.init();  // Reuses cached session from bunq1
+
+// This prevents "Superfluous authentication" errors when multiple instances
+// try to authenticate with the same OAuth token
+
+// Cache management methods
+BunqAccount.clearOAuthCache();  // Clear all cached OAuth sessions
+BunqAccount.clearOAuthCacheForToken('token', 'PRODUCTION');  // Clear specific token
+const cacheSize = BunqAccount.getOAuthCacheSize();  // Get current cache size
 ```
 
 ### Error Handling